Semiconductor device

ABSTRACT

A semiconductor device has a first substrate and a second substrate. The first substrate has first electrodes on at least one surface. The second substrate has concave portions on a surface, and second electrodes provided on bottom surfaces of the concave portions. The semiconductor device further has metallic members located between the first electrodes of the first substrate and the second electrodes of the second substrate. The metallic members have a height greater than a depth of the concave portions of the second substrate, and electrically and mechanically bond the first electrodes of the first substrate and the second electrodes of the second substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2003-297733, filed Aug. 21, 2003,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device constituted by acombination of substrates.

2. Description of the Related Art

U.S. Pat. No. 6,519,075,B2 discloses a technique that connects anelectrostatically driven MEMS mirror array obtained by processing asemiconductor substrate to connection pads of another substrate providedwith an actuator electrode by use of a solder ball (solder bump). FIG.13 shows a semiconductor device manufactured in such a manner.

This semiconductor device has a mirror layer 20 and an actuator layer23. The mirror layer 20 has surrounding frames 22, and gimbaled mirrors21 allowed to incline with respect to the surrounding frames 22. On theother hand, the actuator layer 23 has actuator electrodes 24 to actuatethe mirrors 21. The mirror layer 20 and the actuator layer 23 both havemetallization regions 25, and the metallization regions 25 of the mirrorlayer 20 and the metallization regions 25 of the actuator layer 23 arebonded by the solder balls 26.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a semiconductor device comprising acombination of at least two substrates. The semiconductor device of thepresent invention has a first substrate and a second substrate. Thefirst substrate has first electrodes on at least one surface. The secondsubstrate has concave portions on a surface, and second electrodesprovided on bottom surfaces of the concave portions. The semiconductordevice further has metallic members located between the first electrodesof the first substrate and the second electrodes of the secondsubstrate. The metallic members have a height greater than a depth ofthe concave portions of the second substrate, and electrically andmechanically bond the first electrodes of the first substrate and thesecond electrodes of the second substrate.

Advantages of the invention will be set forth in the description whichfollows, and in part will be obvious from the description, or may belearned by practice of the invention. Advantages of the invention may berealized and obtained by means of the instrumentalities and combinationsparticularly pointed out hereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is an exploded perspective view of an MEMS deflecting mirror,which is a semiconductor device in a first embodiment of the presentinvention;

FIG. 2 is a sectional view of the MEMS deflecting mirror along the lineII-II indicated in FIG. 1;

FIG. 3 shows an alternative embodiment applicable in place of concaveportions shown in FIG. 1 and FIG. 2;

FIG. 4 shows an application of the semiconductor device in the firstembodiment;

FIG. 5 is an exploded perspective view of an MEMS deformable mirror,which is the semiconductor device in a second embodiment of the presentinvention;

FIG. 6 is a sectional view of the MEMS deformable mirror along the lineVI-VI indicated in FIG. 5;

FIG. 7 shows an application of the semiconductor device in the secondembodiment;

FIG. 8 is a sectional view of an MEMS high frequency switch, which isthe semiconductor device in a third embodiment of the present invention,in which a switch is in an off-state;

FIG. 9 is a sectional view of the MEMS high frequency switch, which isthe semiconductor device in the third embodiment of the presentinvention, in which the switch is in an on-state;

FIG. 10 is a sectional view of the MEMS deflecting mirror, which is thesemiconductor device in a fourth embodiment of the present invention;

FIG. 11 is a sectional view of the MEMS deflecting mirror, which is thesemiconductor device in a fifth embodiment of the present invention;

FIG. 12 is a sectional view of the MEMS deformable mirror, which is thesemiconductor device in a sixth embodiment of the present invention; and

FIG. 13 shows a semiconductor device manufactured by use of a techniquedisclosed in U.S. Pat. No. 6,519,075,B2.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will hereinafter be describedreferring to the drawings.

First Embodiment

The present embodiment is directed to an MEMS deflecting mirror. Detailsof the MEMS deflecting mirror are disclosed in U.S. Pat. No.6,519,075,B2 and the like.

FIG. 1 is an exploded perspective view of the MEMS deflecting mirror,which is a semiconductor device in a first embodiment of the presentinvention. FIG. 2 is a sectional view of the MEMS deflecting mirroralong the line II-II indicated in FIG. 1.

As shown in FIG. 1 and FIG. 2, a semiconductor device 100 comprises amirror substrate 110, a wiring substrate 130 located to face the mirrorsubstrate 110, and metallic members 150 bonding the mirror substrate 110and the wiring substrate 130.

The mirror substrate 110 is a substrate that is manufactured bysubjecting a silicon substrate to micro fabrications such as etching andcoating and forming electrodes and wires thereon in accordance with anMEMS technique.

The mirror substrate 110 comprises a frame member 112, a movable mirror114, and two hinges 116 connecting the frame member 112 and the movablemirror 114. The hinges 116 are torsionally deformable, so that themovable mirror 114 is allowed to swing with respect to the frame member112 on the hinges 116. Thus, the movable mirror 114 constitutes amovable portion that mechanically operates. The movable mirror 114 has areflective surface on its upper surface (surface opposite to the wiringsubstrate 130). The reflective surface may be, for example, a surface ofa highly reflective film that is separately provided on the uppersurface of the movable mirror 114.

The wiring substrate 130 has concave portions 132 on a surface facingthe mirror substrate 110. For example, the wiring substrate 130 is madeof silicon, and the concave portions 132 are formed by wet etching.

The wiring substrate 130 further has electrodes 134 provided on bottomsurfaces of the concave portions 132, electrode pads 136 provided at anend of an upper surface of the wiring substrate 130 for electricconnection to the outside, and wires 138 electrically connecting theelectrodes 134 and the electrode pads 136. Electrodes 134, an electrodepad 136, and a wire 138 that are continuous are formed by the sameconductive thin film.

The wiring substrate 130 further has two actuator electrodes 144provided in a part that faces the movable mirror 114 of the mirrorsubstrate 110, electrode pads 146 provided at an end of the uppersurface of the wiring substrate 130 for electric connection to theoutside, and wires 148 electrically connecting the actuator electrodes144 and the electrode pads 146. An actuator electrode 144, an electrodepad 146, and a wire 148 that are continuous are formed by the sameconductive thin film.

The two actuator electrodes 144 are spaced apart, and the space islocated directly under the hinges 116 of the mirror substrate 110 andextends along the hinges 116 of the mirror substrate 110.

As shown in FIG. 2 in particular, the mirror substrate 110 further has aconductive thin film 118 on a surface facing the wiring substrate 130.The conductive thin film 118 expands over a part covering the framemember 112, the movable mirror 114 and the hinges 116. A part of theconductive thin film 118 located on the movable mirror 114 constitutes amirror electrode to exert a driving force that swings the movable mirror114. Parts of the conductive thin film 118 located on the frame member112 constitute electrodes for electric conduction to the electrodes 134of the wiring substrate 130. Parts of the conductive thin film 118located on the hinges 116 constitute wires that electrically connect theelectrode on the movable mirror 114 and the electrode on the framemember 112.

As shown in FIG. 2 in particular, the metallic members 150 have a heightgreater than a depth of the concave portions 132 of the wiring substrate130. The metallic members 150 are bumps made of, for example, gold, andare provided between the electrodes 134 provided on the bottom surfacesof the concave portions 132 of the wiring substrate 130, and parts ofthe conductive thin film 118 located on the frame member 112 of themirror substrate 110. The bumps 150 are pressure-welded with heat toelectrically and mechanically bond the electrodes 134 provided on thebottom surfaces of the concave portions 132 of the wiring substrate 130and the parts of the conductive thin film 118 located on the framemember 112 of the mirror substrate 110.

The semiconductor device 100 is manufactured, for example, as follows.First, the bumps 150 made of, for example, gold are formed by use of abump bonder at predetermined positions in the parts of the conductivethin film 118 on the frame member 112 of the mirror substrate 110. Next,the mirror substrate 110 is fixed on a stage of a flip chip bonder sothat the bumps 150 turn upward. Then, the wiring substrate 130 is stuckto a mounting head and positioned so that the actuator electrodes 144 ofthe wiring substrate 130 properly face the movable mirror 114 of themirror substrate 110. In this state, the electrodes 134 provided in theconcave portions 132 of the wiring substrate 130 also properly face thebumps 150 formed on the mirror substrate 110. Next, hot pressure welding(heating and pressurization) is performed to connect the bumps 150 andthe electrodes 134 on the bottom surfaces of the concave portions 132.

In the semiconductor device 100 thus manufactured, the conductive thinfilm 118 provided on the mirror substrate 110 is electrically connectedby the bumps 150 to the electrodes 134 provided on the bottom surfacesof the concave portions 132 of the wiring substrate 130. The electrodes134 are electrically connected to the electrode pads 136 through thewires 138. Thus, the electrode pads 136 are connected to a ground, sothat potentials of the movable mirror 114 and the conductive thin film118 will be 0.

If a voltage is applied to an actuator electrode 144 in this state,electrostatic attraction is produced between the actuator electrode 144and the part of the conductive thin film 118 on the movable mirror 114,that is, the mirror electrode, and the movable mirror 114 is inclined(deflected) on the hinges 116.

The electrostatic attraction rapidly decreases as the distance betweenthe movable mirror 114 and the actuator electrode 144 increases. Thus,if the distance between the movable mirror 114 and the actuatorelectrode 144 is large, a significantly high voltage is needed toprovide a predetermined inclination to the movable mirror 114. A largepower supply is needed to obtain the significantly high voltage.Moreover, the significantly high voltage might exceed a limit ofdielectric breakdown to break the MEMS.

Therefore, in a configuration in which concave portions are not formedas that of U.S. Pat. No. 6,519,075,B2, the height of the bumps increasesthe distance between the mirror substrate and the wiring substrate.

Contrarily, in the semiconductor device of the present embodiment,because the concave portions 132 are formed in the wiring substrate 130,the distance between the mirror substrate 110 and the wiring substrate130, that is, the distance between the mirror electrode and the actuatorelectrodes 144 is reduced owing to the height of the bumps 150. Thismakes it possible to reduce a required drive voltage.

Furthermore, if the mirror substrate 110 is directly bonded to thewiring substrate 130, the movable mirror 114 contacts the wiringsubstrate 130 when the movable mirror 114 is inclined, and does notfunction as the deflecting mirror.

In the present embodiment, the substrates are connected by the hotpressure welding of the bumps, and resins such as adhesives andanisotropic conductive pastes or films are not used, so that thefunction of the MEMS is not impaired by outward flowing or running ofthe resins.

In addition, the bumps ensure that the mirror electrode and the movablemirror 114 are electrically connected to the ground.

As has been described so far, in the present embodiment, in thesemiconductor device in which the substrates are affixed together, theconcave portions are formed in the wiring substrate, so that the properspace can be provided between the substrates and that the electricconnection can be achieved in all the bumps.

As a result, it is possible to obtain a semiconductor device such as theMEMS device with a low operating voltage and less fear of breakage.

The present embodiment is not limited to the configuration describedabove, and various modifications and alterations may be made.

The silicon substrate processed as a semiconductor substrate has beendescribed as an example in the present embodiment, but various materialsthat enable the micro fabrication such as chemical or physical etchingand wiring formation can be selected for the substrate.

Furthermore, in the case of the gold bump, a stud bump, a plated bump orthe like is applicable. The material of the bump is not exclusivelylimited to gold but may be a conductive metal, and for example, lead-tinsolder, AuSn solder or In (indium) solder is also applicable.

It is important that the material of the electrodes on the surfaces ofthe substrates to be connected by the metallic members is selected inaccordance with the metallic members to be applied. A gold electrode ismost suitable for the gold bump, and aluminum, nickel, titanium, copperor the like is also applicable. Portions near surfaces of the electrodesare preferably made of a conductive material that has satisfactorymutual diffusibility with gold when gold is connected to the electrodes.A proper selection for the material of the electrode improvesanti-reflow properties and heat resisting properties of the substrateand enables the substrate to be subjected to reflow-treatment later.Moreover, if the bump is solder, a material having satisfactory leakageproperties into the solder is usefully formed on an uppermost surface ofthe electrode.

The substrates are bonded by the hot pressure welding, but supersonicwaves may be added as required in the hot pressure welding. In thiscase, effects of compatibility between the materials to be bonded can bereduced, thus providing such anticipated benefits as more freedom in thecombination of the material of the electrode and the material of themetallic members, and a lower heating temperature.

Furthermore, in the above description, the concave portion 132 istotally surrounded at a portion lower than the upper surface of thewiring substrate 130 (i.e., the bottom surface) as shown in FIG. 1 andFIG. 2, but the concave portion 132 is not limited to this form and maybe in a form where the portion lower than the upper surface of thewiring substrate 130 extends to an edge of the wiring substrate 130,that is, a step 142, as shown in FIG. 3. When the concave portion 132 isthe step 142, the same advantages as described above can also beprovided.

Application to the First Embodiment

The present application is directed to arraying of the semiconductordevices including the MEMS deflecting mirrors described above. FIG. 4shows an application of the semiconductor device in the firstembodiment. In FIG. 4, members indicated by the same reference numeralsas those of the members shown in FIG. 1 and FIG. 2 are the same and willnot be described in detail.

The deflecting mirror can be manufactured as the MEMS in a semiconductorprocess, so that a mirror array 110A in which an array of the movablemirrors 114 is formed is produced and connected to the concave portions132 of the wiring substrate 130 by use of the bumps 150, therebyenabling an MEMS deflecting mirror array to be obtained.

Such a mirror array is useful in configuring a large-scale opticalswitch as in U.S. Pat. No. 6,690,885,B1, for example.

In the present application, the bumps are formed in the concaveportions, so that even in a large-scale array in which connectionprobability of the bumps tends to be lower due to an inclination errorin the substrates caused by the increase in the size of the substrates,all the bumps can achieve secure connection and the distance between thesubstrates can be reduced, thus making it possible to reduce theoperating voltage.

The arrayed devices need electric circuits such as control amplifiers tobe drive voltage sources of deflectors corresponding to the number ofarrays, and the size and cost of the amplifiers greatly vary dependingon a required voltage, so that the reduction of the drive voltage isalso effective in the reduction of size and cost of a whole drivecircuit device.

In the present application, the number of bumps 150 is increased as thescale of the array is enlarged, but the concave portions are preformedin parts where the bumps are connected to further ensure that all thebumps achieve connection.

Second Embodiment

The present embodiment is directed to an MEMS deformable mirror. TheMEMS deformable mirror is a device that can change the curvature of themirror thin film portion by use of the electrostatic attraction betweenthe electrode of the mirror thin film portion and the actuatorelectrode, for example, as disclosed in U.S. Patent Application KOKAIPublication No. 2002/0057506 A1.

FIG. 5 is an exploded perspective view of the MEMS deformable mirror,which is the semiconductor device in a second embodiment of the presentinvention. FIG. 6 is a sectional view of the MEMS deformable mirroralong the line VI-VI indicated in FIG. 5.

As shown in FIG. 5 and FIG. 6, a semiconductor device 200 comprises amirror substrate 210, a wiring substrate 230 located to face the mirrorsubstrate 210, and the metallic members 150 bonding the mirror substrate210 and the wiring substrate 230.

The mirror substrate 210 comprises a frame member 212 having an opening,a deformable mirror 214 located in the opening of the frame member 212,and a conductive thin film 218 connecting the frame member 212 and thedeformable mirror 214. The mirror substrate 210 is manufactured from asemiconductor substrate such as a silicon substrate, for example, by anMEMS technique.

The deformable mirror 214 has a reflective surface on its upper surface(surface opposite to the wiring substrate 230). The deformable mirror214 can easily deform together with a part of the conductive thin film218 located in the opening of the frame member 212, so as to change thecurvature of its reflective surface. That is, the deformable mirror 214constitutes a movable portion that mechanically operates.

The wiring substrate 230 has concave portions 232 on a surface facingthe mirror substrate 210. For example, the wiring substrate 230 is madeof silicon, and the concave portions 232 are formed by wet etching.

The wiring substrate 230 further has electrodes 234 provided on bottomsurfaces of the concave portions 232, electrode pads 236 provided at anend of an upper surface of the wiring substrate 230 for electricconnection to the outside, and wires 238 electrically connecting theelectrodes 234 and the electrode pads 236. Electrode 234, an electrodepad 236, and a wire 238 that are continuous are formed by the sameconductive thin film.

The wiring substrate 230 further has an actuator electrode 244 providedin a part that faces the deformable mirror 214 of the mirror substrate210, an electrode pad 246 provided at an end of the upper surface of thewiring substrate 230 for electric connection to the outside, and a wire248 electrically connecting the actuator electrode 244 and the electrodepad 246. The actuator electrode 244, electrode pad 246, and wire 248,which are continuous, are formed by the same conductive thin film.

As shown in FIG. 6, the conductive thin film 218 traverses the openingof the frame member 212, and expands on an entire lower surface of theframe member 212. A part of the conductive thin film 218 located on thedeformable mirror 214 constitutes a mirror electrode to exert a drivingforce that swings the deformable mirror 214. Parts of the conductivethin film 218 located on the frame member 212 constitute electrodes forelectric conduction to the electrodes 234 of the wiring substrate 230. Apart of the conductive thin film 218 located between the deformablemirror 214 and the frame member 212 supports the deformable mirror 214,and functions as a wire to electrically connect the electrode on thedeformable mirror 214 to the electrode on the frame member 212.

As shown in FIG. 6, the metallic members 150 have a height greater thana depth of the concave portions 232 of the wiring substrate 230. Themetallic members 150 are bumps made of, for example, gold, and areprovided between the electrodes 234 provided on the bottom surfaces ofthe concave portions 232 of the wiring substrate 230 and the parts ofthe conductive thin film 218 located on the frame member 212 of themirror substrate 210. The bumps 150 are pressure-welded with heat toelectrically and mechanically bond the electrodes 234 provided on thebottom surfaces of the concave portions 232 of the wiring substrate 230and the parts of the conductive thin film 218 located on the framemember 212 of the mirror substrate 210.

In the semiconductor device 200 thus manufactured, the conductive thinfilm 218 provided on the mirror substrate 210 is electrically connectedby the bumps 150 to the electrodes 234 provided on the bottom surfacesof the concave portions 232 of the wiring substrate 230. The electrodes234 are electrically connected to the electrode pads 236 through thewires 238. Thus, the electrode pads 236 are connected to the ground, sothat potentials of the deformable mirror 214 and the conductive thinfilm 218 will be 0.

If a voltage is applied to the actuator electrode 244 in this state, theelectrostatic attraction is produced between the actuator electrode 244and the part of the conductive thin film 218 on the deformable mirror214, that is, the mirror electrode, and the deformable mirror 214deforms into a concave shape to change the curvature of the reflectivesurface.

As has already been described in the first embodiment, the electrostaticattraction rapidly decreases as the distance between the deformablemirror 214 and the actuator electrode 244 increases. Thus, if thedistance between the deformable mirror 214 and the actuator electrode244 is large, a significantly high voltage is needed to deform thedeformable mirror 214 into a predetermined shape. A large power supplyis needed to obtain the significantly high voltage. Moreover, thesignificantly high voltage might exceed a limit of dielectric breakdownto break the MEMS.

Especially, as the deformable mirror does not have a less elastic partsuch as the hinges in the deflecting mirror, its drive voltage tends tobe high.

In the semiconductor device of the present embodiment, because theconcave portions 232 are formed in the wiring substrate 230, thedistance between the mirror substrate 210 and the wiring substrate 230,that is, the distance between the mirror electrode and the actuatorelectrode 244 can be smaller than the height of the bumps 150. Thismakes it possible to reduce a required drive voltage.

On the other hand, in order to deform the deformable mirror 214 into thepredetermined shape, it is necessary to secure a distance correspondingto the predetermined shape between the deformable mirror 214 and theactuator electrode 244. Especially in an electrostatically drivendeformable mirror, an amount of deformation of the deformable mirror isgenerally reduced to one third of an initial space between thedeformable mirror and the actuator electrode to avoid a pull-inphenomenon wherein the deformable mirror totally contacts the actuatorelectrode. Thus, the deformable mirror 214 and the actuator electrode244 need to be separated three times as much as the deformation amountof the deformable mirror 214.

After all, the distance between the deformable mirror 214 and theactuator electrode 244 is desirably adjusted to a proper value inaccordance with a design in view of the amount of the drive voltage andthe deformation amount of the deformable mirror 214. Moreover, anoptimum value of the distance between the deformable mirror 214 and theactuator electrode 244 is usually smaller than the height of the bumps.

In the semiconductor device of the present embodiment, the initialdistance between the deformable mirror 214 and the actuator electrode244 can be brought to the optimum value by the metallic members 150 suchas the gold bumps and the concave portions 232 formed in the wiringsubstrate 230 and also by controlling pressurization applied when themirror substrate 210 and the wiring substrate 230 are bonded.

In the present embodiment, the substrates are connected by the hotpressure welding of the bumps, and resins such as adhesives andanisotropic conductive pastes or films are not used, so that thefunction of the MEMS is not impaired by outward flowing or running ofthe resins.

As has been described so far, in the present embodiment, in thesemiconductor device in which the substrates are affixed together, theconcave portions are formed in the wiring substrate, so that the properspace can be provided between the substrates and the electric connectioncan be achieved in all the bumps.

As a result, it is possible to obtain a semiconductor device such as theMEMS device with a low operating voltage and less fear of breakage.

The present embodiment is not limited to the configuration describedabove, and various modifications and alterations may be made.

The various modifications described in the first embodiment can beapplied to the materials of the substrate, the bump and the electrode.As also described in the first embodiment, the supersonic waves may beadded as required in the hot pressure welding of the substrates.Moreover, the modifications described in the first embodiment can beapplied to the form of the concave portion 232. Thus, the concaveportion 232 may be in a form (the step 142) where the portion lower thanthe upper surface of the wiring substrate extends to the edge of thewiring substrate as shown in FIG. 3.

Application of the Second Embodiment

This application is directed to the arraying of the semiconductordevices including the MEMS deformable mirrors described above. FIG. 7shows an application of the semiconductor device in the secondembodiment. In FIG. 7, members indicated by the same reference numeralsas those of the members shown in FIG. 5 and FIG. 6 are the same and willnot be described in detail.

The deformable mirror can be manufactured as the MEMS in thesemiconductor process, so that a mirror array 210A in which an array ofthe deformable mirrors 214 is formed is produced and connected to theconcave portions 232 of the wiring substrate 230 by use of the bumps150, thereby enabling an MEMS deformable mirror array to be obtained.Such a device is particularly useful in an image display device or thelike.

In the present application, the bumps are formed in the concaveportions, so that even in a large-scale array in which connectionprobability of the bumps tends to be lower due to an inclination errorin the substrates caused by the increase in the size of the substrates,all the bumps can achieve secure connection and the distance between thesubstrates can be reduced, thus making it possible to reduce theoperating voltage.

The arrayed devices need electric circuits such as the controlamplifiers to be drive voltage sources of the deflectors correspondingto the number of arrays are needed, the size and cost of the amplifiersgreatly vary depending on a required voltage, so that the reduction ofthe drive voltage is also effective in the reduction of size and cost ofthe whole drive circuit device.

In the present application, the number of bumps 150 is increased as thescale of the array is enlarged, but the concave portions are preformedin parts where the bumps are connected to further ensure that all thebumps achieve connection.

Third Embodiment

The present embodiment is directed to an MEMS high frequency switch. TheMEMS high frequency switch is disclosed in U.S. Pat. No. 6,307,452,B1and the like. Operation of the MEMS high frequency switch of the presentembodiment is basically similar to that of a device disclosed in U.S.Pat. No. 6,307,452,B1.

FIG. 8 and FIG. 9 are sectional views of the MEMS high frequency switch,which is the semiconductor device in a third embodiment of the presentinvention, and FIG. 8 shows the switch in an off-state and FIG. 9 showsthe switch in an on-state.

As shown in FIG. 8 and FIG. 9, a semiconductor device 300 comprises aswitch substrate 310, a wiring substrate 330 located to face the switchsubstrate 310, and the metallic members 150 bonding the switch substrate310 and the wiring substrate 330.

The switch substrate 310 comprises a frame member 312 having an opening,and an MEMS cantilever 314 extending from the frame member 312 into theopening. The MEMS cantilever 314 comprises an aluminum thin film 322, aninsulating support thin film 324, and an aluminum thin film 326, whichare laminated in order on a bottom surface of the frame member 312. Theswitch substrate 310 is manufactured from a semiconductor substrate suchas a silicon substrate, for example, by the MEMS technique.

The MEMS cantilever 314 is elastically deformable, so as to displace itsfree end up and down. Thus, the MEMS cantilever 314 constitutes amovable portion that mechanically operates. Moreover, a part of thealuminum thin film 322 located on the MEMS cantilever 314 constitutes anelectrode to exert a driving force that operates the MEMS cantilever314.

The aluminum thin film 322 extends to an end of the frame member 312,while the support thin film 324 and the aluminum thin film 326 terminateat the midpoint of the frame member 312. Therefore, the aluminum thinfilm 322 is exposed at the end of the frame member 312.

The wiring substrate 330 has a concave portion 332, a concave portion334, and a concave portion 336 on a surface facing the switch substrate310. For example, the wiring substrate 330 is made of silicon, and theconcave portion 332, the concave portion 334, and the concave portion336 are formed by wet etching.

The wiring substrate 330 further has a conductive thin film 342extending between a bottom surface of the concave portion 332 and anupper surface of the wiring substrate 330, a conductive thin film 344extending between a bottom surface of the concave portion 334 and theupper surface of the wiring substrate 330, and a conductive thin film346 extending between a bottom surface of the concave portion 336 andthe upper surface of the wiring substrate 330.

A part of the conductive thin film 342 located on the bottom surface ofthe concave portion 332 constitutes an electrode for conduction to thealuminum thin film 326. Similarly, a part of the conductive thin film344 located on the bottom surface of the concave portion 334 constitutesan electrode for conduction to the aluminum thin film 326. Moreover, apart of the conductive thin film 346 located on the bottom surface ofthe concave portion 336 constitutes an electrode for conduction to thealuminum thin film 322.

Accordingly, on the side of the switch substrate 310, a part of thealuminum thin film 322 exposed at the end of the frame member 312constitutes an electrode for conduction to the conductive thin film 346.Further, a part of the aluminum thin film 326 located on the framemember 312 constitutes an electrode for conduction between theconductive thin film 342 and the conductive thin film 344.

The concave portion 332 and the concave portion 334 has the same depth,and the concave portion 336 is shallower than the concave portion 332and the concave portion 334 by a level difference produced by thealuminum thin film 322 and the aluminum thin film 326, that is, by thethickness of the support thin film 324 and the aluminum thin film 326.Therefore, a space between the part of the conductive thin film 342located on the bottom surface of the concave portion 332 and thealuminum thin film 326, a space between the part of the conductive thinfilm 344 located on the bottom surface of the concave portion 334 andthe aluminum thin film 326, and a space between the part of theconductive thin film 346 located on the bottom surface of the concaveportion 336 and the aluminum thin film 322 are all equal.

In FIG. 8 and FIG. 9, the concave portion 334 and the concave portion336 are continued from each other. Thus, the concave portion 334 and theconcave portion 336 constitute one large concave portion having twobottom parts of different depths in a sense. However, in the presentspecification, the concave portion having the bottom parts of differentdepths is regarded as plural concave portions to focus attention on thedifference of depth in the bottom parts.

Naturally, the concave portion 334 and the concave portion 336 do notneed to be continuous and may be separated from each other. In otherwords, the concave portion 334 and the concave portion 336 may beindependent concave portions.

The wiring substrate 330 further has an actuator electrode 352, aprotection film 354 covering the actuator electrode 352, and a contactelectrode 356. The actuator electrode 352 and the contact electrode 356are both provided at locations facing the MEMS cantilever 314 of theswitch substrate 310.

The metallic members 150 are provided between the part of the conductivethin film 342 located on the bottom surface of the concave portion 332and the aluminum thin film 326, between the part of the conductive thinfilm 344 located on the bottom surface of the concave portion 334 andthe aluminum thin film 326, and between the part of the conductive thinfilm 346 located on the bottom surface of the concave portion 336 andthe aluminum thin film 322. These metallic members 150 have an equalheight, and a height greater than the depth of the concave portion 332and the concave portion 334 of the wiring substrate 330.

The metallic members 150 are bumps made of, for example, gold, and arepressure-welded with heat to mechanically bond the switch substrate 310and the wiring substrate 330 and electrically bond the electrodes of theswitch substrate 310 and the wiring substrate 330.

The semiconductor device 300 is manufactured, for example, as follows.

For example, starting with an SOI substrate, processes such as resistpatterning, etching and thin film formation are performed to configure amicro MEMS structure, thereby manufacturing the switch substrate 310.

On the other hand, the concave portion 332, the concave portion 334, andthe concave portion 336 that have proper depths are formed in the wiringsubstrate 330 in view of the level difference produced by the aluminumthin film 322 and the aluminum thin film 326 on the switch substrate310.

Next, on the wiring substrate 330, the actuator electrode 352, thecontact electrode 356, the conductive thin film 342, the conductive thinfilm 344 and the conductive thin film 346 are formed, and the protectionfilm 354 is formed if necessary.

Subsequently, the bumps 150 made of, for example, gold are formed on theelectrodes provided on the bottom surfaces of the concave portion 332,the concave portion 334, and the concave portion 336.

Finally, the switch substrate 310 is pressure-welded with heat to thewiring substrate 330 to complete the MEMS high frequency switch.

In the semiconductor device 300, the aluminum thin film 322 provided onthe switch substrate 310 is electrically connected by the bump 150 tothe part of the conductive thin film 346 provided on the bottom surfaceof the concave portion 336 of the wiring substrate 330. The conductivethin film 346 is connected to the ground. Thereby, the aluminum thinfilm 322 of the switch substrate 310 is satisfactorily maintained at aground potential. Moreover, a signal is supplied to the conductive thinfilm 344 (or the conductive thin film 342).

If a voltage is applied to the actuator electrode 352 in this state, theelectrostatic attraction is produced between the actuator electrode 352and a part of the aluminum thin film 322 facing the actuator electrode352. As a result, the aluminum thin film 322, that is, the MEMScantilever 314 is drawn to the actuator electrode 352, and the aluminumthin film 326 contacts the contact electrode 356. Consequently, thecontact electrode 356 and the conductive thin film 344 (or theconductive thin film 342) are electrically connected.

Furthermore, if the application of the voltage to the actuator electrode352 is stopped, the electrostatic attraction between the actuatorelectrode 352 and the aluminum thin film 322 disappears, so that theMEMS cantilever 314 returns to an original shape, with the result thatthe contact electrode 356 and the conductive thin film 344 (or theconductive thin film 342) are electrically disconnected.

Thus, the voltage application to the actuator electrode 352 can beperformed or stopped to allow or stop a signal flow between the contactelectrode 356 and the conductive thin film 344 (or the conductive thinfilm 342).

In the present embodiment, the concave portions are provided in theparts of the wiring substrate 330 where the bumps 150 are provided, sothat a space between the switch substrate 310 and the wiring substrate330 can be reduced. This allows the distance between the aluminum thinfilm 322 and the actuator electrode 352 to be reduced, and the voltageapplied to the actuator electrode 352 can thus be reduced. Moreover, adrive distance of the support thin film 324 is decreased to enhance anoperating speed.

In the present embodiment, as the difference of distance between thebonded surfaces of the substrates in the connected parts is corrected inview of the thickness of the aluminum thin film 322, the support thinfilm 324 and the aluminum thin film 326, the depth of the concaveportions (step) is changed correspondingly. That is, the depth of theconcave portions (step) is properly changed depending on the place sothat all the spaces between the connected parts are uniform.

As measures for differences in shape of the members that decrease theconnection probability of the bump, including difference in initialheight of the bumps and difference in distance between the connectedparts depending on the place, the concave portions are provided toreduce the effect of the difference in the height of the bumps, and thedepth of the concave portion is changed depending on the place to solvethe difference in distance between the connected parts.

As a result, the electric connection can be ensured in all the connectedparts.

The present embodiment is not limited to the configuration describedabove, and various modifications and alterations may be made.

The various modifications described in the first embodiment can beapplied to the materials of the substrate, the bump and the electrode.As also described in the first embodiment, the supersonic waves may beadded as required in the hot pressure welding of the substrates.Moreover, the modifications described in the first embodiment can alsobe applied to the form of the concave portion. Thus, the concave portionmay be in the form (the step 142) where the portion lower than the uppersurface of the wiring substrate extends to the edge of the wiringsubstrate as shown in FIG. 3.

A manufacturing process has been shown as an example in the presentembodiment wherein the bumps 150 are provided on the side of the wiringsubstrate 330, but the semiconductor device may be manufactured in amanufacturing process in which the bumps 150 are provided on the side ofthe switch substrate 310, and the semiconductor device thus manufacturedhas the same function and advantage as in the present embodiment.

Furthermore, it is preferable to utilize silicon oxide based on SOI orthe like for the support thin film, but various materials can be used,such as silicon nitride and a polyimide resist.

Two kinds of depths of the concave portions have been shown as anexample in the present embodiment, but it is needless to mention thatmore depth levels can be provided depending on the shape of the surfaceof the frame member.

Still further, a representative example of the electrostatically drivenMEMS high frequency switch has been shown in the present embodiment, butthe present embodiment is applicable to those that can be manufacturedby proximately disposing at least two substrates, including otherelectrostatically driven switches, electromagnetically driven switches,piezoelectrically driven switches and the like.

Fourth Embodiment

The present embodiment is directed to the MEMS deflecting mirrorsimilarly to the first embodiment. FIG. 10 is a sectional view of theMEMS deflecting mirror, which is the semiconductor device in a fourthembodiment of the present invention. In FIG. 10, members indicated bythe same reference numerals as those of the members shown in FIG. 1 andFIG. 2 are the same and will not be described in detail.

A semiconductor device 400 of the present embodiment is analogous to thesemiconductor device 100 in the first embodiment, and is only differenttherefrom in that each of the metallic members 150 to bond the mirrorsubstrate 110 and the wiring substrate 130 comprises two bumps, that is,a bump 152 and a bump 154 as shown in FIG. 10.

In the present embodiment, the semiconductor device 400 is manufacturedas follows. First, the gold bumps 152 are formed on the parts of theconductive thin film 118 located on the frame member 112 of the mirrorsubstrate 110, and the gold bumps 154 are also formed on the electrodes134 provided in the concave portions 132 of the wiring substrate 130.Concretely, the gold bumps are preferably formed by use of the bumpbonder, which is equipment to form bumps from a gold wire. Then, themirror substrate 110 and the wiring substrate 130 are positioned so thatthe gold bumps 152 face the gold bumps 154, and are pressure-welded withheat. Thus the semiconductor device 400 is obtained.

In the present embodiment, the gold bumps are respectively preformed onthe conductive thin film 118 of the mirror substrate 110 and theelectrodes 134 of the wiring substrate 130. In this case, aluminum maybe used for the conductive thin film 118 and the electrodes 134 on thebottom surfaces of the concave portions 132. It has already beencommonly known that gold should not preferably be used in thesemiconductor process, that is, a MEMS process. The use of aluminum ispreferable in this respect.

The substrates are bonded substantially by bonding of the gold bumps,and the gold bumps satisfactorily diffuse heat to each other in the hotpressure welding, so that the mirror substrate 110 and the wiringsubstrate 130 are more firmly bonded.

In the present embodiment, as each of the metallic members 150 comprisethe two bumps, the height is increased, but each of the concave portions132 may be made deeper to reduce the distance between the substrates.

In the present embodiment, the concave portions are preformed in thewiring substrate, so that securer connection can be accomplished by thebumps than has heretofore been possible, and the mirror substrate 110and the wiring substrate 130 can be located with a space smaller thanthe height of the bumps. Further, as the mirror substrate 110 and thewiring substrate 130 can be bonded by the hot pressure welding with thegold bumps without forming gold thin films on the mirror substrate 110and the wiring substrate 130, thus providing an advantage that gold isnot needed in the manufacturing and working processes of thesemiconductor substrate itself.

The present embodiment is not limited to the configuration describedabove, and various modifications and alterations may be made.

The various modifications described in the first embodiment can beapplied to the materials of the substrate, the bump and the electrode.As also described in the first embodiment, the supersonic waves may beadded as required in the hot pressure welding of the substrates.Moreover, the modifications described in the first embodiment can alsobe applied to the form of the concave portion. Thus, the concave portionmay be in the form (the step 142) where the portion lower than the uppersurface of the wiring substrate extends to the edge of the wiringsubstrate as shown in FIG. 3.

The material of the bumps used in combination for each substrate is notlimited to the same material. Various combinations of materials areapplicable if the materials allow the bumps to be bonded together. Forexample, a combination of a gold stud bump and a solder bumpmanufactured from a solder paste is possible, and they can be bondedwith head.

Furthermore, each of the bumps may be not only a two-stage configurationcombining two bumps, but also a configuration with three or more stagescombining three or more bumps. In addition, three or more kinds of bumpsmay be provided. In this case, connectivity is not specifically demandedin the bumps that are separate from each other as long as the bumps thatcontact each other have satisfactory connection, thus enabling variousmaterials to be selected.

Fifth Embodiment

The present embodiment is directed to the MEMS deflecting mirrorsimilarly to the first embodiment. FIG. 11 is a sectional view of theMEMS deflecting mirror, which is the semiconductor device in a fifthembodiment of the present invention. In FIG. 11, members indicated bythe same reference numerals as those of the members shown in FIG. 5 andFIG. 6 are the same.

As shown in FIG. 11, a semiconductor device 500 comprises a mirrorsubstrate 510, a wiring substrate 530 located to face the mirrorsubstrate 510, and the metallic members 150 bonding the mirror substrate510 and the wiring substrate 530.

The mirror substrate 510 comprises a frame member 512 having an opening,concave portions 522 formed in a surface of the frame member 512 facingthe wiring substrate 530, a movable mirror 114 located in the opening ofthe frame member 512, the hinges 116 connecting the frame member 512 andthe movable mirror 114, and a conductive thin film 518 provided on asurface facing the wiring substrate 530.

The mirror substrate 510 is manufactured from a semiconductor materialsuch as silicon in the semiconductor process. The concave portions 522are formed by wet etching, for example. The conductive thin film 518 islocated partially on bottom surfaces of the concave portions 522 formedin the frame member 512.

The wiring substrate 530 has the actuator electrode 144 provided in apart that faces the movable mirror 114 of the mirror substrate 510, anda conductive thin film 542 provided on a surface facing the mirrorsubstrate 510. The wiring substrate 530 is made of, but not specificallylimited to, an insulating inorganic material, for example.

In the mirror substrate 510, a part of the conductive thin film 518located on the movable mirror 114 constitutes a mirror electrode toexert a driving force that swings the movable mirror 114. Parts of theconductive thin film 518 located on the bottom surfaces of the concaveportions 522 of the frame member 512 constitute electrodes for electricconduction to the conductive thin film 542 of the wiring substrate 530.The other part of the conductive thin film 518 functions as a wire toelectrically connect the mirror electrode on the movable mirror 114 andthe electrodes on the bottom surfaces of the concave portions 522.

On the other hand, in the wiring substrate 530, parts of the conductivethin film 542 facing the frame member 512 constitute electrodes forelectric conduction to the parts of the conductive thin film 518 locatedon the bottom surfaces of the concave portions 522 of the frame member512.

The metallic members 150 have a height greater than the depth of concaveportions 522 of the mirror substrate 510. The metallic members 150 arebumps made of, for example, gold, and are provided between parts of theconductive thin film 518 provided on the bottom surfaces of the concaveportions 522 of the mirror substrate 510 and the parts of the conductivethin film 542 provided on an upper surface of the wiring substrate 530.The bumps 150 are pressure-welded with heat to electrically andmechanically bond the conductive thin film 518 on the mirror substrate510 and the conductive thin film 542 on the wiring substrate 530.

Operation of the semiconductor device 500 is totally the same as that ofthe semiconductor device 100 in the first embodiment and will not bedescribed here.

In the present embodiment, the wiring substrate 530 simply has theactuator electrode 144 and the conductive thin film 542 on the flatupper surface. This means that the processes such as the formation ofthe concave portions are not needed in the wiring substrate 530. Thus,the wiring substrate 530 does not particularly need to be asemiconductor substrate, and for example, a pyrex glass may suitably beapplied in terms of cost. On the other hand, the mirror substrate 510 ismade from a silicon substrate as described above.

The mirror substrate 510 and the wiring substrate 530 are thus made ofthe different materials, and therefore have different thermal expansioncoefficients. As a consequence, the bumps are subjected to a shearstress due to a change in outside temperature. However, since the bumpshave the height greater than the gap between substrates, the stress isreduced by shear flexure of the bumps. As a result, a highly durablesemiconductor device can be obtained.

As described above, the present embodiment can ensure high durabilityeven in a configuration in which the substrates made of differentmaterials are bonded. Moreover, the use of different materials canadditionally bring specific effects such as lower costs.

The present embodiment is not limited to the configuration describedabove, and various modifications and alterations may be made.

The various modifications described in the first embodiment can beapplied to the materials of the substrate, the bump and the electrode.As also described in the first embodiment, the supersonic waves may beadded as required in the hot pressure welding of the substrates.Moreover, the modifications described in the first embodiment can alsobe applied to the form of the concave portion. Thus, the concave portionmay be in the form (the step 142) where the portion lower than the uppersurface of the wiring substrate extends to the edge of the wiringsubstrate as shown in FIG. 3.

Furthermore, the use of the pyrex glass for the wiring substrate 530 hasbeen shown as an example to reduce costs in the present embodiment, butthe material of the wiring substrate 530 is not limited thereto and canbe more freely selected, so that various glasses, ceramics orcrystalline materials such as alumina, various semiconductors such asGaAs, metallic substrates and the like are applicable.

For example, the material such as GaAs can be used for application to aparticular electronic device substrate to provide a durablesemiconductor device with higher functions.

A glass epoxy resin substrate, for example, can be applied, but is notentirely preferable because of extremely poor stability in shape causedby temperature and unsecured accuracy of the gap between the substrates.

Sixth Embodiment

The present embodiment is directed to the MEMS deformable mirrorsimilarly to the second embodiment. FIG. 12 is a sectional view of theMEMS deformable mirror, which is the semiconductor device in a sixthembodiment of the present invention. In FIG. 12, members indicated bythe same reference numerals as those of the members shown in FIG. 5 andFIG. 6 are the same.

As shown in FIG. 12, a semiconductor device 600 comprises a mirrorsubstrate 610, a translucent wiring substrate 630 located to face themirror substrate 610, and the metallic members 150 bonding the mirrorsubstrate 610 and the translucent wiring substrate 630.

The mirror substrate 610 comprises a frame member 612 having an opening,concave portions 622 formed in a surface of the frame member 612 facingthe translucent wiring substrate 630, a deformable mirror 214 located inthe opening of the frame member 612, and a conductive thin film 618connecting the frame member 612 and the deformable mirror 214.

The mirror substrate 610 is manufactured from a semiconductor materialsuch as silicon in the semiconductor process. The concave portions 622are formed by wet etching, for example. The conductive thin film 618 islocated partially on bottom surfaces of the concave portions 622 formedin the frame member 612.

The translucent wiring substrate 630 has a translucent actuatorelectrode 644 provided in a part that faces the deformable mirror 214 ofthe mirror substrate 610, and a conductive thin film 642 provided on asurface facing the mirror substrate 610.

The translucent wiring substrate 630 comprises an insulating inorganicmaterial, and is made of, but not specifically limited to, glass, forexample. The glass is preferably an optical glass such as BK-7(manufactured by HOYA-SCHOTT Corporation), a pyrex glass, or the like.Quartz, crystal or the like may be applied depending on a wavelengthband of light to be used.

Furthermore, a conductive thin film of, for example, ITO, which is not aspecific limitation, is preferably applied to the translucent actuatorelectrode 644.

In the mirror substrate 610, a part of the conductive thin film 618located on the deformable mirror 214 constitutes a mirror electrode toexert a driving force that deforms the deformable mirror 214. Parts ofthe conductive thin film 618 located on the bottom surfaces of theconcave portions 622 of the frame member 612 constitute electrodes forelectric conduction to the conductive thin film 642 of the translucentwiring substrate 630. The other part of the conductive thin film 618functions as a wire to electrically connect the mirror electrode on thedeformable mirror 214 and the electrodes on the bottom surfaces of theconcave portions 622.

On the other hand, in the translucent wiring substrate 630, parts of theconductive thin film 642 facing the frame member 612 constituteelectrodes for electric conduction to the parts of the conductive thinfilm 618 located on the bottom surfaces of the concave portions 622 ofthe frame member 612.

The metallic members 150 have a height greater than the depth of concaveportions 622 of the mirror substrate 610. The metallic members 150 arebumps made of, for example, gold, and are provided between parts of theconductive thin film 642 provided on the bottom surfaces of the concaveportions 622 of the mirror substrate 610, and the part of the conductivethin film 642 provided on an upper surface of the translucent wiringsubstrate 630. The bumps 150 are pressure-welded with heat toelectrically and mechanically bond the conductive thin film 618 on themirror substrate 610 and the conductive thin film 642 on the translucentwiring substrate 630.

In the present embodiment, the mirror substrate 610 and the translucentwiring substrate 630 are made of different materials, and therefore havedifferent thermal expansion coefficients. As a consequence, the bumpsare subjected to a shear stress due to a change in outside temperature.However, since the bumps have the height greater than the gap betweensubstrates, the stress is reduced by the shear flexure of the bumps. Asa result, a highly durable semiconductor device can be obtained.

Operation of the semiconductor device 600 is the same as that of thesemiconductor device 200 in the second embodiment, and by applying avoltage across the deformable mirror 214 and the translucent actuatorelectrode 644, the electrostatic attraction can be produced to changethe curvature of the deformable mirror 214.

Furthermore, because the translucent wiring substrate 630 and thetranslucent actuator electrode 644 are optically transparent to visiblelight in the wavelength band of the light to be used, the light canstrike on the deformable mirror 214 via the translucent wiring substrate630 and the translucent actuator electrode 644. In that case, a lowersurface of the part of the conductive thin film 618 located on thedeformable mirror 214 functions as a reflective surface.

An ordinary electrostatically driven deformable mirror can only deformthe reflective surface into a concave surface toward an incident lightas disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101402.

On the contrary, the MEMS deformable mirror 600 of the presentembodiment can also cause the light to enter through the wiringsubstrate 630, and therefore, can also deform the reflective surfaceinto a convex surface toward the incident light. Thereby, a divergingbeam of out-going light can be produced from a parallel beam of incidentlight.

Naturally, the MEMS deformable mirror 600 of the present embodiment canalso deform the reflective surface into a concave surface toward theincident light by causing the light to enter from the opposite side ofthe wiring substrate 630 in the same manner as the ordinary deformablemirrors.

Furthermore, the translucent wiring substrate 630 can usually be appliedas a substitute for a lid called a glass lid or a glass window in anairtight package to directly seal semiconductor elements such as a CPUinto a ceramic cavity package, which packages the semiconductorelements, so that it is not necessary to use a window member separately,thus enabling the simplification of the configuration.

Still further, for example, crystal can be applied to thetranslucent-wiring substrate 630 to utilize as a wavelength plate, and afiltering function including an optical thin film can be provided in asurface of the translucent wiring substrate 630.

It is again unnecessary to separately prepare an optical substrate forthe optical thin film, and more complex optical functions can beperformed with a simple configuration.

As described above, in the present embodiment, high connectivity can beobtained between the substrates, and particularly, the use of thetranslucent wiring substrate makes it possible to obtain opticalcharacteristics that can not usually be obtained and to obtain complexoptical performance with the simple configuration.

As described above, even when the substrates made of different materialsare laminated, the present invention can ensure high durability, and,for example, optical properties opposite to ordinary optical propertiesand particular effects such as lower costs can additionally be obtainedby using the translucent material.

The present embodiment is not limited to the configuration describedabove, and various modifications and alterations may be made.

Since there are materials indicating various translucencies to light ofvarious wavelengths, various materials can be applied to the translucentwiring substrate 630. More specifically, an optical crystal such asoptical glass, quartz, crystal, LN, LT or sapphire can be applied to thematerial of the translucent wiring substrate 630 depending on thewavelength.

Furthermore, other optical functions can also be added, and a photoniccrystal or a light guide substrate can be applied to the translucentwiring substrate to add further optical functions.

Moreover, the material of the drive wire is not limited to ITO, and aconductive organic thin film, a silicon thin film or the like can beproperly selected depending on the wavelength of the light desired to beused, and such a modification of the shape of the electrode is alsoeffective that the electrode is positioned on a periphery of an opticaleffective region to avoid a decrease in optical performance.

While the embodiments of the present invention have so far beendescribed with reference to the drawings, the present invention is notlimited to these embodiments, and various modifications and alterationsmay be made without departing from its spirit.

In other words, the above-described embodiments may be properlycombined, partially omitted or have various other elements added theretowithout changing the spirit and concept of the invention.

For example, not only the two substrates but also more substrates may bebonded to constitute the semiconductor device. The number and locationof metallic members used for bonding are properly set as required.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventionconcept as defined by the appended claims and their equivalents.

1-16. (canceled)
 17. A semiconductor device comprising: a firstsubstrate having first electrodes formed on at least one surface; asecond substrate having concave portions on a surface, the concaveportions having flat bottom surfaces, and second electrodes provided onthe bottom surfaces of the concave portions; and metallic memberslocated between the first electrodes of the first substrate and thesecond electrodes of the second substrate, the metallic memberselectrically and mechanically bonding the first electrodes of the firstsubstrate and the second electrodes of the second substrate, so thateach of the metallic members has a first contact portion contacting withone of the first electrodes and a second contact portion contacting withone of the second electrodes, and a minimum distance between the firstand second contact portions being larger than a minimum distance betweenthe surfaces of the first and second substrates.
 18. The semiconductordevice according to claim 17, wherein one of the first substrate and thesecond substrate comprises a semiconductor substrate, and thesemiconductor substrate has a movable portion that mechanicallyoperates, and a third electrode to exert a driving force that operatesthe movable portion.
 19. The semiconductor device according to claim 18,wherein the first electrodes are located at different heights from thesurface of the first substrate, and the concave portions have differentdepths so that all spaces between the first electrodes and the secondelectrodes are equal.
 20. The semiconductor device according to claim18, wherein the first substrate and the second substrate are made ofmaterials having different thermal expansion coefficients.
 21. Thesemiconductor device according to claim 18, wherein the material of thesecond substrate is a semiconductor, and the material of the firstsubstrate is an insulating inorganic material.
 22. The semiconductordevice according to claim 21, the semiconductor device being directed toan application to an optical system, wherein the material of the firstsubstrate is a material having optical transparency in a wavelength bandof light to be used.
 23. The semiconductor device according to claim 18,wherein each of the metallic members comprises at least two metallicportions in a direction in which the substrates are spaced.
 24. Thesemiconductor device according to claim 18, wherein the material of themetallic members is gold, and portions near surfaces of the firstelectrodes and the second electrodes are made of a conductive materialthat has satisfactory mutual diffusibility with gold when gold isconnected to the first electrodes or the second electrodes.
 25. Thesemiconductor device according to claim 24, wherein at least one of thefirst electrodes and the second electrodes is gold.
 26. Thesemiconductor device according to claim 17, wherein the first electrodesare located at different heights from the surface of the firstsubstrate, and the concave portions have different depths so that allspaces between the first electrodes and the second electrodes are equal.27. The semiconductor device according to claim 17, wherein the firstsubstrate and the second substrate are made of materials havingdifferent thermal expansion coefficients.
 28. The semiconductor deviceaccording to claim 17, wherein the material of the second substrate is asemiconductor, and the material of the first substrate is an insulatinginorganic material.
 29. The semiconductor device according to claim 28,the semiconductor device being directed to an application to an opticalsystem, wherein the material of the first substrate is a material havingoptical transparency in a wavelength band of light to be used.
 30. Thesemiconductor device according to claim 17, wherein comprise themetallic members comprises at least two metallic portions in a directionin which the substrates are spaced.
 31. The semiconductor deviceaccording to claim 17, wherein the material of the metallic members isgold, and portions near surfaces of the first electrodes and the secondelectrodes are made of a conductive material that has satisfactorymutual diffusibility with gold when gold is connected to the firstelectrodes or the second electrodes.
 32. The semiconductor deviceaccording to claim 31, wherein at least one of the first electrodes andthe second electrodes is gold.